A systematic study of Thlaspi s.l. taxa in the sections Nomisma, Thlaspi and Pterotropis from Turkey based on fruit morphological and molecular data

Abstract

The classification of Thlaspi s.l. is still problematic. Earlier phylogenetic research of the genus focused on several small groups within Thlaspi s.str. and lacked detailed morphological observations. The relationships among Eurasian taxa and the value of fruit morphology in defining them have yet to be studied. The aim of this study was to analyze 22 taxa belonging to the Nomisma, Thlaspi and Pterotropis sections of Thlaspi s.l. from Turkey using maximum likelihood (ML) analysis of internal transcribed spacer (ITS) sequences. We also analyzed the morphological features of the fruit. According to the results, the examined taxa fell into 2 main clades. Moreover, clade II showed 3 sub-clusters. Thlaspi huetii and T. aghricum were the most distant taxa with a distance of 0.49%; however, T. ochroleucum and T. violascens were found to be 99% similar. According to ITS region data based on multiple populations of each taxon, T. arvense, T. huetii, T. perfoliatum, T. violascens, T. cataonicum, T. elegans, T. rosulare and T. aghricum were placed together in one cluster, which indicates that they are monophyletic. Thlaspi elegans was found to be a polyploid complex based on bootstrap (BS) (a resampling technique that uses replacement sampling to estimate statistics in a population) values, which varied widely among the studied T. elegans taxa (98, 65 and 49%). Fruit morphology also supported the inter-specific relationships based on molecular data, and relationships found by ITS region data were compatible with fruit type and geographic distribution. A diagnostic key based on fruit morphology is provided for the identification of the examined Thlaspi taxa.